Influence of framework Al density in chabazite zeolites on copper ion mobility and reactivity during NOx selective catalytic reduction with NH3

Revealing the Formation and Reactivity of Cage-Confined Cu Pairs in Catalytic NOx Reduction over Cu-SSZ-13 Zeolites by In Situ UV–Vis Spectroscopy and Time-Dependent DFT Calculation

“…26,60−62 As an example, a very recent study has shown that the mobility and dynamic reactivity of Cu cations during lowtemperature NH 3 -SCR can be regulated by rationalizing the density of Al centers in the zeolite framework. 64 We anticipate these mechanistic insights may also offer opportunities to understand the dynamic formation and catalytic consequence of transient metal complexes in environmental redox catalysis over metal-zeolites, such as selective methane oxidation, CO oxidation, etc.…”

“…These findings provide new insights into the monomeric-to-dimeric Cu transformation for completing the Cu redox cycle during low-temperature NH 3 -SCR catalysis over Cu-SSZ-13. Future activities in the design of the high-performance Cu-SSZ-13 NH 3 -SCR catalyst can thus be directed toward promoted formation of such cage-confined reactive Cu pairs by applying operational in situ pretreatments (such as high-temperature thermal activation in an inert atmosphere, low-temperature treatment in a reducing atmosphere), or by rationally tuning the zeolite framework compositions to adjust the coordinative environment, reducibility, and mobility of Cu ions. ,− As an example, a very recent study has shown that the mobility and dynamic reactivity of Cu cations during low-temperature NH 3 -SCR can be regulated by rationalizing the density of Al centers in the zeolite framework . We anticipate these mechanistic insights may also offer opportunities to understand the dynamic formation and catalytic consequence of transient metal complexes in environmental redox catalysis over metal-zeolites, such as selective methane oxidation, CO oxidation, etc . ,, …”

Effect of Framework Composition and NH3 on the Diffusion of Cu+ in Cu-CHA Catalysts Predicted by Machine-Learning Accelerated Molecular Dynamics

“…The hops between adjacent cha cages are modulated by size exclusion effects and also by the attractive interaction between the positively charged [Cu­(NH 3 ) 2 ] + complexes and the negatively charged framework Al sites. ,,,, Thus, structural properties such as the Al content and distribution, Cu loading, and Brønsted acid site density as well as the interaction of the Cu active sites with the reactants, in particular, NH 3 , might affect the mobility of Cu cations and consequently the NH 3 –SCR–NO x reaction rate. This has been evidenced by recent studies combining catalytic activity tests with operando XAS or EPR spectroscopy, − and ab initio molecular dynamics (AIMD) simulations have been successfully applied to provide atomistic insight into the dynamic nature of the Cu + cations under reaction conditions. ,, …”

Interplay between copper redox and transfer and support acidity and topology in low temperature NH3-SCR

“…Because of the EPR silent nature of Cu I -ions and dimeric Cu intermediates that are involved in OHC, operando EPR cannot be applied to address this half-cycle. In a very recent publication by Gounder and coworkers 49 , the authors demonstrated that increasing the zeolite support Al density leads to systematic increases in both the fraction of Cu I ions that are SCR active and OHC rate constants. Based on this new discovery and the current study, BAS influences both the fractions of SCR active Cu II during RHC and the fractions of SCR active Cu I during OHC.…”